USE OF GEL-FREE ALUMOXANE SOLUTION

Abstract: Disclosed is a method of using gel-free alumoxane solution in the preparation of supported catalysts. These supported catalysts produce polymer particles with excellent morphology and minimal to no reactor fouling during polymerization.

Description: TITLE: USE OF GEL-FREE ALUMOXANE SOLUTION Field of the Invention: This invention relates generally to polymerization catalysts and more particularly to the use of gel-free alumoxane solution as a cocatalyst for supported catalyst useful in the polymerization of olefins. Background of the Invention Alumoxane solution has been known to be a useful cocatalyst with metallocenes in the formation of catalysts. A problem associated with alumoxane is the formation of gel or gel like particles. Problems associated with gelled alumoxane include the gels plugging up reactor lines, enhancing fines or fine formation, creating difficulties in preparation of supported catalysts. US 5,157,137, incorporated by reference, discloses a method for removing gels and providing clear gel-free solutions of alumoxane, and especially methylalumoxane by treating the solution with certain alkali or alkaline earth metals compounds. US '137 discloses that the treatment results in alumoxane solutions that are stable and remain gel-free for extended periods of time. The inventors have found that the use of gelled alumoxane can cause or contribute to fouling in a polymerization reactor. Various supported catalyst techniques employing alumoxane solutions are known. None appear to disclose or distinguish between the use of gelled versus gel-free alumoxane. Summary of the Invention This invention relates to a method in which visually clear, substantially transparent, gel-free alumoxane solution (AO) is used in the preparation of polyolefins comprising the step of removing gels from a gelled alumoxane solution, or alternately separating gels from AO with gels and using the substantially gel-free AO during the polymerization of olefins to polyolefins. The invention further relates to a method for producing a supported catalyst comprising combining visually clear, substantially gel-free alumoxane (AO) obtained by separating gelled-AO from AO containing gelled particles with a dehydrated carrier and at least one metallocene to form a supported catalyst. The invention further relates to a method for the polymerization of olefins to polyolefins combining contacting the supported catalyst prepared as described above with at least one olefin under suitable polymerization conditions, wherein the olefin contains from 2 to about 20 carbon atoms. The gel-free alumoxane is preferably methylalumoxane employed in a ratio of aluminum in the alumoxane to transition metal in the metallocene of about 12: 1 to about 1000: 1, preferably in a ratio of about 100: 1 to about 500: 1. An alternate embodiment of this invention relates to a method to make a controlled particle size polyolefin comprising the steps of: a. removing gels from a gelled alumoxane solution and combining the gel- free alumoxane solution with a dehydrated support and at least one metallocene to form a supported catalyst. A further alternate embodiment relates to a method for preparing a supported catalyst comprising of the steps of (a) acquiring a gelled alumoxane solution from a vendor; (b) removing gels from said alumoxane solution; and (c) combining the substantially gel-free alumoxane solution of (b) with a support and a metallocene to yield a supported catalyst. A still further embodiment relates to a method for preparing a supported system comprising the steps of: (a) separating gels from a gelled AO solution to yield a substantially gel- free AO solution (b) combing the solution of (a) with a support and a metallocene, said combining step occurring no more than seven days subsequent to the completion of step (a). The invention is useful with any class of transition metal compounds or metallocenes including mono, di, or tri cyclopentadienyl radical systems or derivatives thereof. Monocyclo-pentadienyl moieties include, for example, those as disclosed in US 4,808,561 or US 5,055,438 herein incorporated by reference. Carriers include organic or inorganic support mediums. Particularly preferred carriers include porous, inorganic mediums such as silica, alumina or silica alumina combinations with silica being the most preferred. Supported catalysts made with gel-free alumoxane solutions generally produce polymer having excellent morphology, controlled particle size, generally in granular form, with minimal to no fouling occuring in the reactor during polymerization. Detailed Description of Perferred Embodiments US 4,808,561, US 5,240,894 and, US 4,921,825 disclose various methods of supporting transition metal components or metallocenes employing alumoxane as a cocatalyst. There are many publications on the use of alumoxane as a cocatalyst in the preparation of supported catalysts. The references identified above are a representative sample. While there are methods reporting on producing gel-free alumoxane, none appear to address the use of or advantages from using gel-free alumoxane or methylalumoxane (MAO). It is common practice in the art to shake up gelled solutions so as to uniformly distribute all particles. We have found that use of a uniformly distributed gelled alumoxane solution can yield a supported catalyst which produces agglomerated polymer. U.S. 5,157,137 discloses a method to avoid gels forming in an alumoxane solution. We have found that one can remove the gels and use the gel-free alumoxane solution without further treatment to produce a supported catalyst with excellent performance relative to that produced with gelled alumoxane solutions. The alkali treatment disclosed in US '137 is not necessary for use of the alumoxane solutions especially if the gel-free alumoxane is used immediately upon separation. The alkali treatment disclosed in US '137 adds cost to the alumoxane. By eliminating the treatment, a more cost efficient catalyst may be produced. The present invention describes a method of using alumoxane free of unnecessary additives or additional treatment steps. Since alumoxane will gel over time, it is preferred to use the separated gel-free alumoxane within about 5-7 days after separation, preferably about 3-5 days, and most preferably immediately upon separation to about 2 days for 10 wt.% alumoxane solutions. If employing 30wt.% alumoxane it is generally advised to use the separated alumoxane within about 3-5 days, preferably about 1-3 days and most preferably immediately upon separation to about 1 day. The alumoxane solution may be purchased from a vendor, for example, Ethyl Corporation or Shering Corporation, or can be produced before use via known literature techniques. The inventors have discovered that polymer particles with excellent morphology are produced from silica supported catalyst made from gel-free alumoxane. In addition, use of gel-free alumoxane solution in the preparation of the catalyst results in minimal to no reactor fouling during the polymerization reaction. Still further, the use of gel-free alumoxane results in minimal to no polymer agglomeration. A comparative example employing gelled alumoxane yielded a supported catalyst which produced fouling in the reactor and clumped polymer. US '561, US '825 and US '894 each describe various methods of producing a supported catalyst. A modification of the technique described in US '894 is the preferred embodiment for the production of the supported catalyst. A preferred embodiment for forming a supported catalyst comprises the steps of contacting a substantially gel-free alumoxane solution, at least one metallocene, and a dehydrated carrier or support medium. The supported catalyst is optionally prepolymerized with alpha olefins. US '894 is silent on the use of gel-free alumoxane. The present invention represents an improvement over that described in US '894. "Substantially gel-free" is defined as a visually clear, substantially transparent alumoxane solution absent of haze and gels. In the alternative, gelled alumoxane is defined as a translucent alumoxane solution containing haze and gels. The color of the alumoxane solution is not relevant here provided the solution is substantially transparent, free of haze and gels. For purposes of this invention , one of skill in the art will appreciate that techniques for monitoring the gel particles in the alumoxane solution, other than visual, will suffice. For example, alternative monitoring techniques including light beam transmission would be suitable for determining "gel-free" state of alumoxane. Once the alumoxane solution has become gelled or cloudy, it is preferred to let the contents of the container settle. A physical separation of the gel-free alumoxane from the gel like material may be achieved by conventional techniques such as physical withdrawal or by extraction by a syringe. The gel particles may be removed by filtration, separating the filtrate from the solution or be removed by other conventional liquid-solid separation techniques such as centrifugation and decanting the liquid. Metallocenes represented by the general formula below may be employed with the gel-free alumoxane solution. Cp m MR n Xq wherein Cp is a cyclopentadienyl ring or derivative thereof, M is a Group 4, 5, or 6 transition metal, R is a hydrocarbyl group or hydrocarboxy group having from 1 to 20 carbon atoms, X is a halogen, and m=l-3, n=0-3, q=0-3, and the sum of m+n+q will be equal to the oxidation state of the transition metal. The metallocene may be bridged or unbridged, and include heteroatoms in the structure. Preferred metallocenes are represented by the general formula: wherein: M 1 is a metal of group 4, 5, or 6 of the Periodic Table, R 1 and R 2 are identical or different, are one of a hydrogen atom, a C Cio alkyl group, a Ci-Cio alkoxy group, a -CIQ aryl group, a C 6 -Cι 0 aryloxy group, a C 2 -C]o alkenyl group, a C 7 -C4 0 arylalkyl group, a C 7 -C4 0 alkylaryl group a Cg-C4o arylalkenyl group, or a halogen atom; R 3 and R 4 are hydrogen atoms; R 5 and R 6 are identical or different, preferably identical, are one of a halogen atom, a CJ-CJO alkyl group, which may be halogenated, a C 6 -C 10 aryl group, which may be halogenated, a C2-Cj 0 alkenyl group, a C -C Q -arylalkyl group, a C 7 -C 0 alkylaryl group, a C 8 -C 0 arylalkenyl group, a -NR 2 15 , -SR 15 , - OR 15 , -OSiR 3 15 or -PR 2 15 radical, wherein R 13 is one of a halogen atom, a | C Cio alkyl group, or a -CJQ aryl group; R 7 is RU RU RU RU RU M 2 -,- M 2 - M 2 -,- M 2 -(CR 2 13 )-,-O- M 2 -O I R 12 R 12 R 12 R 12 R 12 RU RU C - , - O - M 2 - I I Rl 2 R' 2 =BR 11 ,=A1R 11 , -Ge-, -Sn-, -O-, -S-, = SO, =SO 2 , =NR π , =CO, PR 11 , or =P(O)R 1 ] ; wherein: R 11 , R 12 and R 13 are identical or different and are a hydrogen atom, a halogen atom, a Cι-C 2 o alkyl group, a Cι-C 20 fluoroalkyl group, a C6-C30 aryl group, a C5-C30 fluoroaryl group, a C ] -C Q alkoxy group, a C -C Q alkenyl group, a C7-C4 0 arylalkyl group, a Cg-C 0 arylalkenyl group, a C 7 -C 0 alkylaryl group or R 11 and R 12 , a C7-C40 alkylaryl group, or R 1 l and R 13 , together with the atoms binding them, can form ring systems; M 2 is silicon, germanium or tin, or a derivative thereof; R 8 and R 9 are identical or different and have the meanings as stated for RU; m and n are identical or different and are zero, 1 or 2, m plus n being zero, 1 or 2; and the radicals R 10 are identical or different and have the meanings stated for R 11 , R 12 and R 13 or two adjacent R 10 radicals can be joined together to form a ring system. Examples of particularly preferred metallocene components include rac-dimethylsilandiylbis (2-methyl-4, 5-benzoindenyl) -zirconium dichloride; rac-dimethylsilandiylbis (2-methylindenyl) -zirconium dichloride; rac-dimethylsilandiylbis (2-methyl-4, 6-diisopropylindenyl) -zirconium dichloride; and rac-dimethylsilandiylbis (2-methyl-4-phenylindenyl) -zirconium dichloride. Exemplary metallocenes include monocyclopentadienyl titanocenes such as pentamethylcyclopentadienyl titanium trichloride, and the like, dimethylsilyl(tetramethylcyclopentadienyl)(t-butylamido)zirconium dimethyl (or dichloride) and the like, biscyclopentadienyl zirconocenes such as biscyclopentadienylzirconium dichloride and the like. In accordance with the preferred embodiment for forming the supported catalyst, the support is dehydrated preferably at about 800°C for about 18-24 hours or until a 1% or less loss on ignition value is obtained. Prior to use, the supported catalyst is dried to remove essentially all of the residual solvent which may be trapped in the pores of the carrier. This results in a free-flowing supported catalyst. Once the supported catalyst is formed, it may be employed under various polymerization conditions. Suitable polymerization conditions include gas phase, or slurry polymerization. In a preferred embodiment the supported catalyst prepared as described herein is contacted with alpha olefins in a slurry polymerization reactor. The invention is further illustrated by the following non limiting examples. Experimental All experiments were carried out in nitrogen purged dry boxes. All solvents were purchased from commerical sources and were nitrogen purged or distilled and dried over activated molecular sieves. Aluminum alkys were purchased as 20-25 wt% solutions from commercial sources. The MAO was purchased as 30 wt% in toluene from Shering corporation. The polymerization procedure is as follows. In a clean, dry two liter autoclave which had been flushed with propylene vapor, triethylaluminum, TEAL, (about 0.8 ml, about 1.5 M in heptane) was added and then the reactor closed and filled with about 750 ml liquid propylene. With the reactor temperature at about 30°C the catalyst (as a 25 wt% oil slurry) was washed in via an addition tube with about 250 ml propylene. The reactor was rapidly heated to about 65°C. After thirty minutes the reactor was cooled and the excess propylene vented. The polymer was removed and dried. Polymer analysis was carried out as described in US 5,026,798 and US 5,017,714. DSC melting points were determined on commercial DSC instruments and are reported as the second melting point. DMS (MBI) ZrCl 2 = dimethylsilandiyl bis(2-methyl-4, 5-benzoindenyl) zirconium dichloride. Preparation of DMS (MBI) ZrCl 2 : Diethyl methyl (2-naphthylmethyl) malonate (1 ) 5.15 g (224 mmol) of sodium were dissolved in 150 ml of absolute ethanol, while heating, and 37.3 ml (217 mmol) of diethyl methylmalonate were added at room temperature. A solution of 50 g (217 mmol) of 2-bromomethylnaphthalene (96% pure) in 270 ml of ethanol was slowly added dropwise at 0°C, and the mixture was heated under reflux for a further 4 to 5 hours. It was poured onto ice- water and extracted with ethyl acetate. The combined organic phases were dried with sodium sulfate and evaporated. After drying under an oil pump vacuum, the oily residue was stirred with hexane at 0°C, whereupon 55 g (81%) of the compound 1 crystallized. Synthesis of 2-Methyl-3-naphthylpropionic acid (2) A solution of 23.7 g (422 mmol) of potassium hydroxide in 50 ml of water was added to 33.2 g (105 mmol) of the compound 1 in 70 ml of ethanol, and the mixture was heated under reflux for 4 hours. After the solvent had been stripped off, the solid residue was taken up in ethyl acetate, water was added and the pH was brought to 1 with hydrochloric acid. The aqueous phase was extracted several times with ethyl acetate. After drying over magnesium sulfate, the combined organic phases were evaporated completely. The residue was stirred with hexane for crystallization. For decarboxylation, the beige-colored solid was heated at 175°C until the evolution of gas had ended. 21 g (94%) of the product 2 were obtained as a beige-colored solid. Synthesis of 2-Methyl-6.7-benzoindan-l -one (3) 22 ml of thionyl chloride were added to 21 g (98 mmol) of the compound 2, with exclusion of moisture, and the mixture was heated under reflux for 30 minutes. Excess thionyl chloride was then distilled off. The residue was briefly freed from volatile compounds under an oil pump vacuum and then dissolved in 25 ml of methylene chloride, under Ar as an insert gas. The solution was slowly added dropwise to a suspension of 26 g (196 mmol) of aluminum trichloride in 60 ml of methylene chloride and the mixture was heated under reflux for a further 30 minutes. It was poured onto ice and extracted with methylene chloride. The combined organic phases were dried with sodium sulfate and evaporated. The dark oily residue was chromatographed on 600 g of silica gel 60. 8.6 g (45%) of the compound 3 were able to be eluted (yellowish solid) with a mobile phase mixture of hexane/ethyl acetate (9:3). Synthesis of 2-Methyl-4.5-benzoindene (4) 2.2 g (59.5 mmol) of sodium borohydride were added in portions to a solution of 7.8 g (39.7 mmol) of the indanone, compound 3 in 400 ml of a tetrahydrofuran/methanol mixture (2: 1) at room temperature, and the mixture was stirred for 14 hours. The solution was poured onto HCL-acid ice and extracted with ether. The combined organic phases were washed several times with water and dried with sodium sulfate. The orange-colored oil which remained after the solvent had been stripped off was dissolved in 240 ml of toluene, and the solution was heated at 80°C with 570 mg (3.15 mmol) of p-toluene-sulfonic acid for 15 minutes. It was washed several times with water at room temperature, dried with sodium sulfate and evaporated. The residue was chromatographed on 300 g of silica gel 60. 4.7 g (65%) of the indene 4 were able to be eluted (colorless oil) with a mobile phase mixture of hexane/diisopropyl ether (20:1). 1H-NMR spectrum (360 MHz, CDCL3): 8.02 (l,d), 7.84 (l,m), 7.59 (l,d), 7.52 (l,d), 7.38-7.48 (2,m), 7.06 (l,m), 3.42 (2,s), 2.25 (3,d). Synthesis of Dimethylbis(2-methyl-4. 5-benzoindenyl) silane (5) 10.2 ml (25.5 mmol) of a 2.5 M butyllithium solution in hexane were added to a solution of 4.6 g (25.5 mmol) of the compound 4 in 50 ml of tetrahydrofuran at room temperature, and the mixture was heated under reflux for 1 hour. The red solution was then added dropwise to a solution of 1.55 g (12 mmol) of dimethyldichlorosilane in 10 ml of tetrahydrofuran at room temperature, and the mixture was heated under reflux for 5 to 6 hours. The reaction solution was poured onto ice-water and extracted several times with ether. The combined organic phases were dried with sodium sulfate and evaporated, and the residue was dried under an oil pump vacuum. It was chromatographed on 300g of silica gel 60. 500 mg of unreacted starting compound 4 were initially able to be eluted with a mobile phase mixture of hexane/3% ethyl acetate. The ligand system, compound 5, then followed with the same mobile phase. After the solvent had been stripped off, this ligand system was crystallized (isomers) from hexane. The yield was 1.7 g (34%, or 44% with respect to the indene, compound 4 reacted). Synthesis of rac - Dimethylsilanediylbis (2-methyl-4.5-benzo-indenyl) zirconium dichloride (6) 4.0 ml (10.2 mmol) of a 2.5 M butyllithium solution in hexane were added to a solution of 1.7 g (4.1 mmol) of compound 5 in 20 ml of tetrahyrofuran at room temperature under Ar as an inert gas, and the mixture was stirred at room temperature for 14 hours. The residue which remained after the solvent had been stripped off was dried using an oil pump vacuum and washed with hexane. The pale brown powder obtained was dried using an oil pump vacuum at 40 to 50°C for several hours and added to a suspension of 1.0 g (4.0 mmol) of zirconium tetrachloride in 25 ml of methylene chloride at -78°C. After the mixture had been warmed to room temperature, the solvent was stripped off and the residue was extracted with 20 ml of toluene in order to remove the meso form of the metallocene, compound 6. The residue of the toluene extract was then extracted with 40 ml of methylene chloride. The solution was concentrated to a small volume and left to crystallize at -35°C. A total of 970 mg (42%) of the ziroconcene, compound 6 were isolated in several fractions as the pure racemate. 1H-NMR spectrum of the racemate (300 MHz, CDCL3): 7.96 (2,m), 7.78 (2,m), 7.60 (2,d), 7.48-7.56 (4,m), 7.36 (2,d), 7.27 (2,s,b-Ind-H), 2.37 (6,s,Ind-CH3), 1.36 (6,s,Si-CH3). Mass spectrum: 574 M+, correct disintegration, correct isotope pattern. Gel-free MAO was employed. A freshly separated solution of gel-free MAO, decanted from a solution of gelled MAO was employed. Example 1 : To a filtered solution of metallocene DMS (MBI) ZrCl 2 (0.05g) in toluene (75 ml) the gel-free, decanted MAO supernatant solution (30 wt.% MAO, 5.3 ml) was added with stirring. After ten minutes the solution was red-orange and clear. To this was added dehydrated silica (6.0g, Davison 948 regular, about 800°C dehydration) and stirred about fifteen minutes. This slurry was evaporated on a rotoevaporator at about 40°C over about twenty five minutes at which point the slurry had reached a "mud" stage. After an additional twenty minutes drying at about 45°C the solids were recovered as a light orange solid (6.59g). Example 2: To a filtered solution of metallocene, DMS (MBI) ZrCl 2 (O. lg) in toluene (50 ml) the clear, decanted MAO supernatant solution (30wt.% MAO, 10.6 ml) was added with stirring. After ten minutes the solution was red-orange and clear. To this was added dehydrated silica (2.0g, Davison 948 regular, 800°C dehydration) and stirred about fifteen minutes. This slurry was filtered and the solids dried on a rotoevaporator at 50°C. The filtrate was repeatedly added back to the solids as it dried. Final drying at 60°C gave a red-orange solid. (2.53g). Comparative, Gel containing MAO catalyst preparation: Example 3 : To a filtered solution of metallocene DMS (MBI) ZrCl 2 (0.05g) in toluene (75mls), gelled MAO slurry resulting from uniformly agitating the bottle (30wt.% MAO, 5.3ml) was added with stirring. After five minutes the solution was red- orange and slightly hazy. To this was added dehydrated silica (6.0g, Davison 948 regular, 800°C dehydration) and stirred about 15 minutes. This slurry was evaporated on a rotoevaporator at about 44°C over about 25 minutes at which point the slurry reached a "mud" stage. After about thirty five minutes additional drying at about 46°C, the solids were recovered as a light orange solid. (7.2g) Polymerizations were conducted at about 65°C, under the conditions described above with the catalysts of examples 1, 2 and 3. Polymerizations with the catalysts of examples 1 and 2 resulted in free flowing, granular polymer with minimal to no residue observed on the walls of the reactor. Polymerization with the catalyst of example 3 resulted in polymer clumping and residue detected on the walls of the reactor. The clumping of the polymer made it impractial to determine particle size. The results of the polymerization runs are noted in Tables 1 and 2 below. Table 1 Results of Examples 1-3 a) To give approximately the same Zr amount for each run. Table 2 Particle Size Distribution The examples demonstrate that the use of gel-free alumoxane solution results in (1) a supported catalyst which produces polyolefins with improved morphology relative to that obtained using gelled alumoxane solution and, (2) minimum to no fouling in the polymerization reactor. This is in contrast to use of gelled alumoxane solution which resulted in a supported catalyst producing polymer clumping on the agitator and walls of the polymerization reactor and wherein the polymer was not free flowing or granular in form. The description of preferred embodiment has been set forth merely to illustrate the invention and is not intended to be limiting. Upon reading the disclosure, those skilled in the art will appreciate and understand that modification or variations of the described embodiment will not depart from the spirit and substance of the invention. Although the preferred embodiments herein are related to heterogeneous polymerization conditions, the separated, gel-free alumoxane may also be usefully employed under homogeneous polymerization conditions.

Claims: Claims 1. A method to use gelled alumoxane (AO) in the preparation of polyolefins comprising the step of removing the gels and using the substantially gel-free AO solution during the polymerization of olefins to polyolefins. 2. A method for producing a supported catalyst comprising the steps of (a) removing gels from a gelled alumoxane (AO) solution and combining the resulting solution with; (b) a dehydrated support, and (c) at least one metallocene to form a supported catalyst. 3. A method for polymerization of olefins to polyolefins comprising the step of contacting the supported catalyst obtained by the method of claim 2 with at least one olefin under suitable polymerization conditions. 4. The method of claim 3 wherein the olefin contains from 2 to about 20 carbon atoms. 5. The method of any one of the preceding claims wherein the alumoxane is methylalumoxane and wherein the methylalumoxane is employed in a ratio of aluminum in the alumoxane to transition metal in the metallocene component of 12:1 to 1000:1, pereferably 100: 1 to 500:1. 6. A method for preparing a supported catalyst system comprising the steps of: (a) separating gels from a gelled AO solution to yield a substantially gel- free AO solution (b) combining the gel-free solution of (a) with a support and a metallocene, said combining step occurring no more than seven days subsequent to the completion of step (a).

Inventors: BRANDLEY WILLIAM BARRY, BURKHARDT TERRY JOHN, BRANDLEY, WILLIAM, BARRY, BURKHARDT, TERRY, JOHN
Applicants: EXXON CHEMICAL PATENTS INC, EXXON CHEMICAL PATENTS INC.
Application year: 1994
Main classification: C07F5
IPC codes: B01J31, B01J37, C07F5, C08F4, C08F10